UK aero wheel brand Parcours has a new aero gravel wheelset out. Called the FKT (standing for Fastest Known Time), it’s used the Panaracer GravelKing X1 in 40mm width as its partner tyre in its aero testing.
Parcours says that most of the best gravel bike wheels aim to mitigate the negative impact of wide gravel bike tyres, with their more aggressive tread pattern than a road bike tyre. In contrast, it claims to have aero optimised the gravel tyre/wheel combo.
Parcours compares the benefits of its FKT wheels fitted with GravelKing X1 tyres to the difference between riding a time trial bike with climbing wheels and with a deep front/disc rear combination.
Draggy tyres
The combination of width and tread is a significant limiting factor in aero optimising gravel bike wheels, Parcours says.
When DT Swiss, SwissSide and Continental launched their new Aero 111 road bike front tyre, their solution was an almost slick tyre with small cavities to trip the airflow and generate turbulence to promote adherence of the air flowing over the rim and thus reduce drag.
The knobs on a gravel bike tyre have the opposite effect, Parcours found, generating drag. Its wind tunnel testing showed that the knobblier the tyre, the more the drag.
When it wind tunnel tested the Schwalbe G-One RS Evo Race, WTB Riddler and Pirelli Cinturato RC X on its rims, it found that there was an increase in drag relative to the GravelKing X1 of 10.0 watts, 14.1 watts and 15.3 watts respectively at 48km/h.
Parcours attributes this mainly to the higher side knobs on these tyres than on the GravelKing X1. It reckons that this would equate to between 4 and 6 minutes added to ride time at Unbound.
Parcours says that there’s another significant constraint on aero optimising wheels for gravel bike tyres: the tyres’ width. Its wind tunnel testing for its road bike wheels suggests that the best aero performance is achieved when the height of the rims is around four times their width. This would imply a rim depth of 120mm for a 40mm wide gravel tyre.
Since no-one’s going to race gravel on 120mm deep rims, Parcours has designed its rim profile to be aero at a more manageable 47mm deep.
Another problem addressed by the Parcours FKT wheels’ design is the ETRTO guidelines which recommend a maximum rim internal width of 27mm for 40mm tyres. But it has previously found that aerodynamics are optimised with a rim that’s slightly wider than the tyre, so the FKT wheels broaden out significantly from the hookless rim, to reach 40mm at their maximum width.
Despite their width, the Parcours FKT wheels have a claimed 1,500g wheelset weight. Unlike Parcours’ road bike wheels, the rim profile is the same in the front and rear wheels, as it found that the wind yaw angles experienced by the front and back wheels were more similar on gravel than on road.
The Parcours FKT wheelset is priced at £1,199 / $1,599 / €1,599 and can be ordered immediately, with delivery in August. Parcours is providing a free pair of Panaracer GravelKing X1 tyres with orders placed in July.
